This invention relates to the forming of materials by extrusion.
Commonly owned British Pat. No. 1,370,894 discloses and claims a process of and apparatus for the forming of materials by extrusion which can be performed continuously provided the feed material is fed in continuously. The said process in broad terms comprises the steps of feeding material into one end of a passageway formed between first and second members with the second member having a greater surface area for engaging the material to be extruded than the first member, said passageway having a blocked end remote from said one end and having at least one die orifice associated with said blocked end, and moving the passageway-defining surface of the second member relative to the passageway-defining surface of the first member in a direction towards the or each die orifice from said one end to said blocked end such that the frictional drag of the passageway-defining surface of the second member draws the material substantially in its entirety along the passageway and through the or each die orifice.
The apparatus referred to in the preceding paragraph in broad terms comprises movable and fixed members defining an elongate passageway therebetween, an abutment member arranged to project into and block the passageway, means defining at least one die orifice leading from the passageway and associated with the abutment member, means for continuously feeding material to be extruded into the passageway at a position spaced from the abutment member, the amount of the surface area of the passageway defined by the movable member being greater than the amount of the surface area of the passageway defined by the fixed member, whereby upon movement of the passageway-defining surface of the movable member relative to the passageway-defining surface of the fixed member, the material fed into the passageway is moved by frictional drag with the surface of the passageway in the movable member towards the abutment member and is thereby extruded substantially in its entirety through the or each die orifice.
A particular form of the said apparatus, disclosed in the said British Pat. No. 1,370,894, comprises a rotatable wheel member having an endless groove therein and constituting the movable member, a stationary shoe member overlying part of the length of the groove, forming a passageway therewith, and constituting the fixed member an abutment member associated with the shoe member and projecting into the groove and blocking one end of the passageway, and at least one die orifice associated with the abutment member or shoe member.
Described in commonly owned British Pat. No. 1,434,201 which is a Patent of Addition to said British Pat. No. 1,370,894, are improvements in the apparatus specified in the preceding paragraph. They include the improvement of the shoe member having a portion projecting into and extending over a length of the passageway in front of the abutment member and of a width substantially equal to that of the passageway. An apparatus so improved is referred to hereafter as "of the hereinbefore specified kind".
If it is desired to change the product size to one which has a dimension bigger than that of the largest dimension of the feed material (the wheel groove being of a size which can handle such size of material), an expedient can be adopted such as is disclosed in commonly owned co-pending British application No. 20120/74, the substance of which is incorporated in commonly assigned U.S. Pat. No. 4,044,587 of Aug. 30, 1977, that is, the passageway has its cross-sectional area changed along its length in the direction from the inlet end thereof to the extrusion die end thereof in a manner such that the cross-sectional area of the passageway is greater at the die end than at the inlet end thereof, so that shape deformation of the feed material occurs during the passage of the material along the passageway, and this allows for extruding to a larger dimension than a dimension of the feed material.
Whilst these expedients are effective, it is nevertheless necessary in practice to employ feed material which is not much less in dimension than that of the product, where an increase in dimension is required. This means in effect that in order to obtain significant variations in product size, a range of feed material sizes have to be used together with a corresponding number of groove sizes, which means employing separate extrusion machines, or changing a wheel to one with a different groove, and changing the shoe member, the abutment member, and the die orifice to suit the new groove size.
In practice, feed materials are produced in very few standard sizes, and it is an object of the present invention to provide apparatus which can be used to produce a variety of product sizes, whilst needing to employ a very small number of machine variants, preferably as few as one only, and employing a standard size of feed material or a minimum number of standard sizes.